Predator Defense and Host Selection Behavior of Billbugs (Coleoptera: Dryophthoridae)

Billbugs are a complex of weevils that feed on the roots of turfgrass, causing severe damage to the plants. These pests are traditionally managed with applications of insecticides. However, there is a need for non-chemical management tools. Here I investigate billbug behavior in relation to two potential avenues for more sustainable management: using resident predators to suppress billbugs (Chapter II) and selecting specific turfgrasses that resist billbug damage (Chapter III). In Chapter II, I investigate the effects of predator presence and cues associated with their presence on billbug behavior. Though resident predators contribute very little to billbug suppression through directly killing and consuming billbugs, I found that the presence of predators caused billbugs to spend less time feeding and mating, and more time on predator avoidance behaviors. Moreover, predator odor alone induced similar changes, suggesting that adult billbug detect predators using their odor. Although predators do not often directly consume billbugs, their presence may still contribute to billbug suppression. My findings also provide the framework for further investigation of predator chemicals as a potential billbug management tool. In chapter III, I examine adult billbug preferences for water stressed turfgrasses, and turfgrass cultivars with different drought resistance traits. I found that billbugs were more abundant in drier areas, and that billbug damage was higher in turfgrass with low drought resistance. While billbugs did prefer some turfgrasses over others, they did not prefer drought stressed or drought susceptible plants. Drought resistant turfgrasses are available to alleviate drought stress and may generally suffer less billbug damage, however, this does not appear to be a function of repelling adult billbugs. Continued evaluation of the factors that drive billbug preferences among turfgrasses, and turfgrass of traits associated with lower billbug damage could guide cultivar development against two key stressors, drought and billbugs, in the Intermountain West. Overall, my research shows that short term changes in turfgrass management practices, such as conserving the natural predator community and selecting specific types of turfgrass, could assist in billbug management. In the long term, investigation of billbug management using predator chemicals and development of turfgrasses that resist billbug damage could form the basis of sustainable billbug management programs.